The present invention relates to the production of refractory materials satisfactory in performance up to temperatures of 1650.degree. C., particularly but not solely in steel melting processes.
Reviews of existing techniques and of developments now underway have been extensively described in the literature for instance by P. Artelt (Trans. Brit. Ceram. Soc. 74 (3) 67, 1975) "Refractories for oxygen steel-making in Germany"; by G. M. Farmery (Steel Times Annual Review, 89, 1968, L17524) "Trends in the Technology of Casting Pit Refractories in the U.K."; and by D. H. Houseman (Steel Times Annual Review 1971) "High Alumina: steelmaking refractory of the future". Present materials now used for these purposes include mullite, alumina chrome magnesite, zircon, and zirconium oxide. Combinations of two or more of these substances are also employed.
These refractory must have a reasonable resistance to thermal shock, that is, they must withstand the temperature cycles common in the steel making process (typically 110.degree. C. to 1750.degree. C. and sometimes then down to ambient temperatures). It is highly desirable that the refractory can undergo an appreciable number of working cycles -- a minimum of 30 being regarded as satisfactory. Statements of some of the more important features of the thermal properties of refractories have been made by e.g. D. P. H. Hasselmann (J. Amer. Ceram. Soc. 57 (10) 1974); by Ainsworth and Herron (Bull. Amer. Ceram. Soc. 153 (7) 1974) and by V. Dauknys, et al ("Science of Ceramics", Vol. 7 1973).
Other properties which have been said to be important include:
I. chemical resistance (with respect to the steel and to the alloying constituents) PA1 Ii. resistance to creep as defined for instance by the B.S. "Creep under load" test and "not modulus of rupture" test (B.S. 1902 Part IA: 1966) PA1 iii. reasonable mechanical strength (as defined for instance by the "Cold rupture" test). PA1 1. They may be sintered to higher density by firing under relatively mild conditions. Trials have shown that the higher activity of comminuted plasma dissociated zircon results in a lowering of firing temperatures for a given firing shrinkage of approximately 150.degree. C. PA1 2. ceramic bodies made from comminuted plasma dissociated zircon is in consequence of their high density less permeable than one made from milled zircon. PA1 3. "Dizirc" bodies are less readily attacked by molten steel-making slags than bodies made from milled zircon by reason of its lower permeability and higher density. PA1 4. The resistance to thermal shock of a "Dizirc" body is better than that of a milled zircon body.
Studies of these properties with particular reference to bonded zircon refractories demonstrating also the high thermal stability associated with good resistance to acid slag and alkalis have been set out by P. C. Budnikoff (Domez, 5 (1), 47-48 (1933)); G. F. Comstock (J. Amer. Ceram. Soc. 16, 12, 1933) and T. S. Busby et al (Glass Techn., 3, No. 6, 190 1962).